To reduce discharge of fuel vapors into the atmosphere, vehicles may include evaporative emission control systems which include a carbon canister coupled to a fuel tank to adsorb fuel vapors. For example, a carbon canister may adsorb refueling, diurnal and running loss vapors during engine off conditions. Such vehicles may periodically perform leak diagnostics on the emission control system to monitor for leaks so that mitigating actions and vehicle maintenance may be performed. In some approaches, vacuum generated during engine operation may be used to perform leak diagnostics.
In hybrid electric vehicle applications, engine run-time may be limited hence a vacuum pump may be used for leak detection during engine off conditions. For example, hybrid electric vehicles may include an evaporative leak detection pump included in an evaporative leak check module (ELCM) in an emission control system, e.g., in a vent path of a fuel vapor canister, which may be used for generating vacuum in the emission control system for leak diagnostics.
Such leak check modules may include an internal reference orifice which may be used to obtain a reference pressure which is used as a pass/fail threshold for leak testing. For example, during a leak test, the pump in the module may evacuate a small volume of air from the emission control system through the internal orifice to obtain the reference pressure. The reference pressure obtained from the reference orifice may assist in compensating for environmental conditions such as temperature, altitude, fuel level, etc., during the leak test. The pump may then be operated to generate decreasing pressure in the emission control system which may be monitored so that a leak is indicated in response to the pressure in the emission control system remaining above the reference pressure.
However, the inventors herein have recognized that controllers in a vehicle with such leak check modules may assume a default orifice size for internal reference orifices in leak check modules. For example, during leak diagnostics the controller may assume that the internal orifice in a leak check module is of a default size or diameter, e.g., 0.02″, and may indicate a leak based on this assumed default size of the orifice. However, diameters of reference orifices in different leak check modules may vary from the default orifice size assumed by the controller. For example, many leak check modules may include reference orifices with diameters less than the default size, e.g., less than 0.02″ in size. This may result in false positive identifications of leaks in the system. For example, if the controller assumes that the reference orifice in a leak test module is the default size when the actual reference orifice size in the module is less than the default size, then leak detection based on a reference pressure obtained from the reference orifice will diagnose leaks less than the default size.
The inventors herein have recognized the above-described issues and, in one example approach, a method for a vehicle with an engine comprises operating a pump to draw air from an emission control system through an orifice to obtain a reference pressure, and indicating a leak in response to pressure in the emission control system remaining above a threshold pressure while operating the pump to decrease pressure in the emission control system, where the threshold pressure is based on a coded indication and the reference pressure. For example, the coded indication may indicate a size of the orifice.
In this way, the actual orifice size, e.g., as measured by a manufacturer of a leak check module, may be included in a coded indication, e.g., stored in a smart chip integral to the leak check module, so that the controller can receive an input of this characterized leak size and adjust its own threshold in software stored in its memory to only flag leaks of the default size and above. Such an approach may reduce false positive identifications of leaks during leak diagnostics by taking into account the unique reference orifice size for each individual leak check module.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.